Telephone system



March 15, 1938. B. A. HENSLER Er AL, 2,110,910

TELEPHONE SYSTEM Filed Aug. 23, 1935 I 4 Sheets-Sheet l Jfrr March 15,1938. B. A. HENSLER ET AL TELEPHONE SYSTEM Filed Aug. 23, 1935 4Sheets-Sheet 2 T ll! Arrx March 15, 1938. 'B A HENSLER AL 2,110,910

TELEPHONE SYS TEM Filed, Aug. 25, 1935 4 Sheets-Sheet 3 U QW 41 5 db;:22 i

March 15, 4-938. B. A. HENSLER El AL 2,110,910

TELEPHONE SYSTEM Filed Aug. 25, 1935 4 Sheets-Sheet 4 fizz/wen Amman r5464015 6%; Xian/4K0 n-519s Patented Mar. 15, 1938 UNITED STATES PATENTosrlcs TELEPHONE SYSTEM Bernard Anthony Peters, London,

mens Brothers & Company England Hensler and Charles Leonard England,assignors to Sie- Limited, London,

'7 Claims.

This invention relates to telephone systems and more particularly to anarrangement suitable for use in a toll or trunk telephone system whereineach incoming call causes a switching apparatus to set itself to aposition indicative of the order of arrival of the call with respect toother calls, the several switching apparatus so set being released inthe order of arrival of the respective calls and are thereupon caused tosearch for a free subsequent circuit as these are rendered available.The setting and release of the switching apparatus may be controlled bya chain of relays which are operated and released respectively tocontrol such operations, and the system may be applied to a toll ortrunk system wherein calls are set up on demand by operators, i. e. ademand system.

A system of this type has already been suggested in which a distributorswitch on being set in motion by an incoming call searches for and testsinto an outlet to a display panel and if other calls are awaitingattention the call is added to a queue, the switches stepping on and somoving the call to the head of the queue as earlier display positionsbecome available. If there are no other calls waiting in a queue and asubsequent circuit is available the distributing switch neverthelesstests into the first display position and is immediately released tosearch for the subsequent circuit.

In the present invention improved call queueing arrangements areprovided by arranging that in moving ,a call up the queue thedistributing switches do not step but a common switching mechanismassociated with the display effects the moving up process by providingfor the release of the switches in the display positions in turn assubsequent circuits become available. This arrangement is especiallyadvantageous where the distributing switches are high speed motor drivenswitches as the step by step action in the queue is avoided. Afurtheradvantage is gained by placing the display positions at the endof the distributing switch bank so that if a subsequent circuit isavailable at a time when there are no calls in the queue a searchingdistributing switch is not stopped momentarily in a display position butproceeds directly to the outlet to the subsequent circuit.

It is, accordingly one feature of the present invention that switchingapparatus taken into use by an incoming call is caused to search for afree subsequent circuit, such as a connecting circuit on an operatorsposition and if this search is unsuccessful to assume a positioncorresponding to the order of thecall with respect to other calls whichhave failed to be connected to subsequent circuits. The severalswitching apparatus are released from such positions in the order of.arrival of the calls as subsequent circuits are rendered available tosearch for these circuits.

According to another feature of the invention switching apparatus takeninto use by incoming calls and formed into a queue remains in the sameposition during the movement of the call to the head of the queue untilit is released to search for a subsequent circuit for the extension ofthe call.

The arrangements on which the incoming calls are thus queued may consistof a number of relays which are operated seriatim as the calls take aposition in the queue, and arrangements maybe provided whereby therelays are picked up in a continuous order of rotation irrespective ofthe actual relative position of a call in a queue.

In the application of the invention to a normal or semi-automatic systemarrangements are provided for giving relief to the demand operators, bysignalling a further operator or operators when more than a certainnumber of calls are queued up. The furtheroperator or operators maynormally deal with other types of incoming calls.

In order toeffect a certain economy modifications tothe system of theprior invention may be made whereby incoming lines are connectable tothe switching apparatus already referred to over a searching switch, theswitching apparatus having full availability ,to the subsequentconnecting circuits.

One method of carrying out the invention is described by Way of examplein the following description of the. arrangements illustrated in theaccompanying drawings, wherein the inven tion is illustrated as appliedto a toll or trunk telephone system in which under normal trafficconditions calls are dealt with in the demand basis. It is to beunderstood that the invention is not confined on its application to suchsystems, but is capable of utilization in any system of calldistribution.

In Fig. l of the drawings are illustrated an incoming line circuit ILC,and a call distributor circuit DD. There is also illustrated a portionof .an operator's cordless. connecting circuit CC, of which there isprovided a number on each position, and a portion of an operatorsposition circuitOPC, only those circuit elements of these lattercircuits necessary to the understanding of the present invention beingshown.

In Fig. 2 is illustrated a lamp display circuit LDC, calling lamps DOPon a demand position and calling lamps OOP demand and incoming on afurther or omnibus position. A further portion of an operators positioncircuit OPC is shown in this figure.

An incoming line circuit ICL Fig. 1 includes a step by step switch oruniselector P having wipers and arcs pl to p5, driving magnet PDM, andinterrupter contacts pdm. The line relay is designated LA, the testrelay TA and a switching relay H. The incoming line, junction or trunkis designated JCT. The arcs p2 and 103 are concerned with the connectionof the speaking wires, the arc pl with the testing circuit, the arc Mfor determining the type of call, i. e. whether it is an ordinary callor one from a coin box. The arc p5 is a homing arc.

The distributor circuit includes a motor driven switch or uniselector Dwith wipers and arcs I, la, 4, 4a, and a latch magnet LM. The circuitfor and the driving motor of the switch being well known per se is notshown.

Each arc of contacts consists of two rows of 52 contacts each, adouble-ended wiper being adapted to traverse the rows in succession. Thearcs are associated in pairs, namely, l and la, 2 and 2a, and so on, andit is arranged that during search when the wipers of an arc havetraversed the contacts in both rows of the are a switching relay WS isoperated to connect the main circuit wire to the wiper of the other areof the pair. The arcs I, and la, and 2, and 2a, are for connectingthrough the positive and negative wires, and the arcs 3, and 3a, and 4,and 4a, are concerned with testing into the connecting circuits.

The connecting circuits at the several operators positions are connectedto the contacts on the several arcs. To the final eleven contacts in thesecond set of contacts of are 401. are connected the wires 1d, and OFwhich lead to the lamp display circuit Fig. 2. Connections are also madefrom certain of the ten contacts in arcs 3a and 2a corresponding to thecontacts of arc to to which the wires ld are connected, the purpose ofthese connections being explained fully hereinafter. The connectingcircuits are commoned over the arcs of the distributor switches of theseveral distributor circuits, the connecting circuits including those ondemand positions, omnibus and other relief positions. There is provideda line relay L, a releasing relay B, a testing relay T, and switchingrelief relays S and SS respectively. The relay TCO is provided fordetermining the origin of a call, e. g. whether it has been originatedover an ordinary line or a call box line. The relay RR is a ringingrelay for applying a ringing current back to a calling party. Thefunctions of relay D8 will be best understood from the subsequentdetailed description, but generally they are to modify the testingcircuit for testing in to the connecting circuits after a call has beenreleased from association with the lamp display circuit.

The portion of the connecting circuit illustrated in Fig. 1 showscontacts SPKI, SPKZ and SPKS of a speaking key and relays SK,.SL, BA,and AS this being the order in which the relays are operated. Thefunctions of the relays Will be best understood from the followingdetailed description. The elements of the operators circuit CPC Figs. 1and 2 include contacts CA! and CA2 of a call answering key, andcontacts. RA (Fig. l) of a release answering key. 'The functions of therelays CG, CN, and MN will be described in detail hereinafter.

The lamp display circuit Fig. 2 includes step by step switches oruniselectors AB and BA. The arcs abl abB of switch AB are shown, butonly the arc ha! of switch BA is shown, the other arcs of the switch BAbeing associated with the lamp multiple extending over the arcs ab6ab8and the method of connection of the multiple t0 the arcs will be readilyunderstood from the consideration of the wiring of arcs ab6-ab8. Themultiple wiring from the arcs ab6ba8 extends to the display lamps lil onthe demand operators positions DOP, and it will be seen that themultiple wires over the arcs are slipped at each are so that the firstcontact of the arc abB is connected to the wire leading to display lampl, the first contact in the arc ab! is connected to the wire leading todisplay lamp 2 whilst the multiple wire to lamp l appears at the secondcontact in the arc and so on over the remaining arcs. The demand lampson the omnibus position OOP are connected in parallel with the lamps onthe demand position DOP.

The are ab'l is concerned with the stepping and homing of the switch AB,and the object of the arcs c122 and ha! is to ensure that the switchesAB and BA are always in alignment, the relay SY controlling the steppingof the switch BA to bring it into alignment with switch AB.

The wires Zdlill from the arc 4a of the distributor switch are connectedseriatim to the relays AJ, contacts of the relays AJ being connectedseriatim to the wipers of arcs ab6 12118.

The functions of the various relays shown will be best understood fromthe subsequent detailed description.

An omnibus position normally deals with incoming calls signalled on theincoming lamps quite independently of the traffic on the demandoperators position "unless excessive congestion exists on the latter,whereupon the incoming lamps on a particular omnibus position orpositions are disconnected and the demand lamps connected up by theoperation of relay AA. Such a condition is indicated to a supervisoryoperator over the lead SP.

The general operations of the arrangements illustrated are as follows:Upon a call being made over a junction or line JCT the switch P in ILCsearches for and tests into a free distributor circuit DD.

Normally one or more demand operators will have a position connectingcircuit assigned which is brought about by throwing the speaking key SPKassociated with the connecting circuit and the call answering key CA inthe position circuit. On the seizing of a distributor circuit DD theswitch D is caused to hunt for an assigned connecting circuit, and whensuch is found the calling party is switched through to the operator whothen sets up the desired connection.

If the call had originated at a call box or over a line demandingspecial treatment, the operator would receive a tone on the originationand switching through of the call, and then cause the conversationalconnection to be set up by throwing a key (not shown) in the connectingcircuit which applies earth to the negative wire.

The operator controls the release of the call and can release it bythrowing either the key REL in the connecting circuit CC or the key RAin the position circuit OPC.

In the event of a call being made whilst a. connecting circuit is notassigned, the distributor switch hunts until afreecircuit over oneof thedisplay leads Id is found and tests into this to cause a calling lamp tolight, and busies the circuit against other searching distributorswitches which will test into the other displaycircuit leads. The callsare thus caused to be queued up in the order of origination, and whenthe display circuit is fu1l,i. e. ten calls arestored," other searchingdistributor switches test into an overflow circuit over the lead OF towhich" the call meter CM is connected at this time to indicate thenumber of calls so held.

An operator causesthe release of the call from the head of the queue bysimply assigning a connecting circuit, the distributor switch associatedwith this call then being released from the display to search for theassigned connecting circuit whereupon the switches AB and BA step tomoveup, in effect, the remaining calls in the queue one in the order oftheir priority of calling. Calls held on the overflow circuit arereleased and one of these tests into the lamp circuit just freed whichnow is so connected as to place the call at the lowest position in thequeue, whilst the other calls are again connected to the overflowcircuit.

If a call is held in the display circuit for more than a predeterminedperiod a timing circuit comes into operation to cause calling lamps tolight on a relief position (over the lead AL Fig.

2) so that a relief operator is signalled. Similarly, in the exampledescribed, a relief operator is signalled if the number of calls in thequeue areaches seven, the relief operator being held until the numberfalls below six; If the number of calls in the queue reaches nine thenthe incoming lamps associated with a particular 10mnibusoperators'position are disconnected, and the demand lamps are connectedin parallel with the lamps on the demand operators position so that theomnibus operator'can assist the demand operator. The omnibus position isdisconnected when the number of calls in the queue falls below eight.

The circuit arrangements illustrated will now a be described in detail.

Assuming that a call is made over an ordinary line, i. e. a:line from anordinary local subscriber or over a local selector, then a loop'will beapplied to the positive and negative wires JCT resulting in theoperation of relay LA over contacts -h4 and n5. At contacts lal earthisuapplied tothe P wire-to busy the line at preceding selectors, if thecall has been made over a selector, and at contacts Za3 the test relayTA is connected to the wiper of the test are p1. A circuit is closedfrom earth over contacts tal, M, 1112, pdm to magnet PDM to battery andmagnet PDM energizes and opens the contacts pdm whereby the abovecircuit 'is broken and the magnet deenergized and the wipers of theswitch are stepped on to the first outlet in their arcs.

If the outlet is busy the relevant contact in arc -.-.pl will be markedbusyby an earth applied from the distributor circuit DD and as aconsequence relay TA'will be short circuited and prevented fromoperating and therefore when the contacts pdm close 'on' thede-energization of themagnet PDM the circuit for the magnet isxagainclosed and the wipers stepped on tothe next outlet in the manner beforedescribed.

A free outlet will be marked by a battery po-. tent-ial over contacts(m2, ssG and bl in the'distributor. circuit DDflzandx-as a,- consequencewhen the wiper pl meets a free outlet relay TA operates from the batterypotential, over are pl, and contacts ms; The driving circuit for themagnet PDM isopened and an obvious circuit is closed for the right-handcoil of relay H at contacts tal. Relay H operates and at contacts hllocks itself temporarily over its left hand coil to earth over contactslal, and at contacts hZ prepares a point in a locking and busyingcircuit over which it locks on the release of relay LA.

At contacts 71.3 a furtherpoint in the driving circuit for magnet PDMisopened. Contacts 116 prepare a circuit for the operation of relay TCOover its coil (I) and arcs p5 and p4, but however as the line calling isan ordinary line no connection is made to the contact in are 124.

At contacts M andn5 relay LA is disconnected, relay LA being slow torelease and does not release immediately and the incoming loop isextended to relay L in DD over contacts rrl and W2 and relay L operates.A circuit is closed for relay B from earth over contacts 885 and ll andrelay B operates. circuit for relays SS and DS, and, contacts 13 preparea holding circuit over the arc pl for holding the circuit ILC. Contactsl4 prepare a supervisory circuit for the supervision of the call.

Upon the operation of relay B an earth is applied over contacts M andare pl to short circuit relay TA, hold relay H, and busy the outlet atthe preceding selector if such has been employed. Relay LA releasesshortly after relay B operates and-disconnects relay TA. Contacts 122connect a ringing signal tone from lead RS and over contacts as? to thepositive wire and thence to the calling party. Contacts b3 close a pointin the circuit for the test relay T.

A circuit is closed from earth over contacts tl, sl, i006, b4, latchmagnet LM to battery and earth, and the latch magnet operates closingcontacts whereby-the circuit of a driving motor is closed, the motor inrotating driving the wipers of the distributor switch in known manner.

Under normal operating conditions, i. e. when calls can be answered ondemand, a connecting circuit, a portion of which is shown in therectangle CC, will be assigned on one or more operators positions, theassignment of a connecting circuit necessitating the throwing of aspeaking key SPK associated with the connecting circuit CC and theconnect answer key CA in the operators circuit OPC. On the closing ofthe contacts SPKZ a circuit is closed from battery over a resistance inthe operators position circuit OPC, the coils of relay SK in series overthe contacts SPKZ, contacts sZl to earth and relay SK operates and atits contacts skl short circuits its left hand coil. A circuit is closedfrom earth over the left hand coil of relay MN in OPC, contacts bal,SPK3, s7c2, relay SL to battery and earth and relays MN and SL operatein series. Contacts .92! hold relay SK over its right hand coil independently of contacts SPKL A battery potential is applied to the contact inthe are 4 or M of the distributor D corresponding to the connectingcircuit, over relay BA, key contacts REL, contacts s13, 8M, key contactsRA and CAl in. OPC, and contacts s12.

Assuming that an assigned connecting circuit exists in the arcs l, 2, 3,4 of the distributor switch D then the wipers of the switch are drivenuntil the wiper of are 4 meets the contact marked by battery over therelay BA, whereupon a circuit is closed from earthscontact enl, (alsoshownin Fig. 2) contacts 120.3, arc and Wiper 3, contacts wsd, s34, ds3,b3, rectifier 7', both coils of relay T in series, contacts ws5 to themarked contacts and relay T operates and at contacts tl opens thecircuit for the latch magnet LM, whereby the wipers of the switch D arebrought to rest, short circuits the upper coil of relay T, and relays Tand BA operate in series. The lower coil of relay T is of low resistanceand the earth over it busies the outlet to the connecting circuitagainst other searching distributors by preventing their T relays fromoperating. At contacts ba2 relay BA locks itself independently ofcontacts 812 and CAI, and at contacts bal disconnects the left hand coilof relay MN and connects in its place the right hand coil of this relayin series with relay CG. Relays SL and MN hold and relay CG operates. Atcontacts 12113 a circuit is prepared for relay AS but this relay cannotoperate in series with the upper coil of relay T owing to thedisposition of the rectifier 1'. Contacts had close the circuit of thesupervisory lamp ASL in front of the operator.

When relay T operates and contacts tl change over, a short circuit isremoved from relay S, and this relay operates in series with the latchmagnet LM, the latch magnet however not being energized suiliciently inthis series circuit to withdraw the latch.

Relay S at contacts sl locks itself independently of the latch magnetand at contacts s2 and s3 prepares to extend the positive and negativeconductors to the connecting circuit CC. Contacts s4 prepare a point ina circuit for relay AS in CC. Contacts 85 do not concern us at present.

A circuit is closed from earth over the 0115 normal contacts onl, whichas the switch is off normal are closed, contacts s5, coil (I) of relayDS, relay SS, resistance to battery and earth, and relays SS and DSoperate.

At contacts es! and over contacts Z2 a locking circuit is closed forrelays SS and DS independently of the contacts onl and .95. Contacts ssZand $33 prepare further points in the positive and negative wires to theconnecting circuit CC.

Contacts 334 connect earth over Z4 and s4, and over 10.94, ba3, relay ASto battery and relay AS operates to disconnect and extinguish thesupervisory lamp ASL at contacts 6052. A locking circuit is closed forrelay AS over contacts as! and SPKl to prevent relay AS being releasedwhilst the speak key is operated. At contacts ss5 an obvious circuit isclosed for relay TCO and the circuit for relay B is opened. Contacts $85perform no function at this stage. Relay TCO operates.

When relay B releases after its slow releasing period the circuit ILC,and the preceding selector if such has been used, are held over contactsbl, $86, and s6 and Z3 in parallel.

On the operation of relay TCO contacts i002 and i003 complete theconnection of the positive and negative wires to the connecting circuit.The other contacts of relay TCO will be referred to hereinafter.

The operator may now converse with the calling party and completes theconnection to the wanted party. The speak key SPK in CC and the key CAin OPC are restored and relays CG, MN, and SL are released at SPK3.Relay SK is released at contacts sZI, and relays BA and T are held overthe contacts ba2 and s13.

When the calling party clears the line, or flashes the operator to callher attention, relay L releases and at contacts 14 opens the circuit forrelay AS in CC, the relay releasing to light the supervisory lamp ASL infront of the operator at contacts cs2.

The operator may release the distributor circuit by operating therelease key RA in OPC or REL in CC and thereby release relay T which atcontacts ti short circuits relay S.

On the release of relays L and S the earth is removed from the privateWire to the circuit ILC, and the preceding selector, and relay H isreleased which at contacts 716 closes an obvious homing circuit for theswitch P.

At contacts 35 the original circuit for relays SS and DS(I) is opened,but these relays remain held over onl, Z2, and ssl, and a homing circuitfor the switch D is closed over onl, 85, b4, LM to battery and theswitch commences to home and when the home position is reached contactson! open disconnecting the circuits for the magnet LM and relays SS andDS. Relays SS and DS release, and relay SS releases relay TCO. Thetesting circuit for the switch P is held open at contacts 0212 until theswitch reaches home. The circuits are now at normal in preparation fordealing with further calls.

If the circuit ILC terminates a call box line the connection from thearc M to the coil (I) of relay TCO over contacts too will be completed,and it will be seen that on the operation of relay SS relay TCO will beprevented from operating over this coil as it is short circuited. As aconsequence: a tone will be given to the operator over contacts i002 andthe positive conductor and the operator on observing such tone throws akey (not shown) in the connecting circuit whereby an earth is applied tothe negative wire and relay TCO is operated over its coil (II) andcontacts tco 3, ss3, and s3.

Relay TCO operates and performs the functions before described.

In the event of the assigned connecting circuit being connected to thearcs la, 2a, 3a and 4a of the switch D, then when the wipers meet thelast contacts in their arcs a circuit is completed from earth lastcontact in arc 3, contacts ws4, ss l, (183, 123, rectifier r, relay T,ws5, last contact in arc 4, (coil (1) of relay WS to battery and relaysT and WS operate. At contacts wsl relay WS locks itself over its coil(II) to contacts on]. At contacts 1082-1085 the arcs I, 2, 3, and 4 aredisconnected and'arcs I 11, 2a, 3a, and 4a are connected up. Contactsws6 prepare to lock relay TCO over its coil (I). The circuit of relayTis opened when contacts ws5 change. over and relay T releases. Relay Tis operated only for a very short time which may be insufiicient toallow relay S to operate. Even so, if relay S does operate relay SS andDS cannot operate as they are short circuited at this time by theconnection of earth over contacts 882, $2, ws2 and are I a, the earth tothe other side of the relays being derived over contacts on! and .95.

The switch now searches over the second half of its arcs for theassigned connecting circuit and when this is found the operations asbefore described take place.

If it is required to ring a calling subscriber who has left the line theoperator throws a ringing key (not shown) in the connecting circuitwhereby a battery potential is applied to the positive wire whichoperates relay RR. At contacts rrl and 772 ringing current over theleads R and RRS is applied to the calling line.

In the event of a connecting circuit not being assigned such as willhappen at busy periods the distributor switch D drivesuntil the wiper ofarc 4a meets the wires ld leading to the lamp display short circuitedover contacts s32, 82, we! and are la. so that they cannot operate.

A circuit is closed from earth over contacts ss3, s3; ws3, arc 2a, coil(II) of relayTCO to battery and relay 'ICO operates and looks overcontacts 'wsl and tool.

At contacts i005 a circuit is closed for relay DS over its coil (II) andcontacts ss5 and relay DS operates Relay B isheld independently-ofcontacts ll. at contacts (152 so that relay B cannot be released inthe-event of the calling party leaving the line.

'When relay A, Fig. 2, operates it closes a locking circuit for itselfat contacts al independently of the arcs'ab3 and M24, and at contacts a2prepares a circuit for relay B. Contacts 13 prepare a point in thecircuit to'the overflow lead OF, but this circuit is not completed untila maximum number of calls arestored on the display. Contacts a4 and allclose in parallel and'completea circuit over arc abt for the callinglamp I on the demand operators position DOP. Relay AC operates inparallel with lamp I and over contacts 3% and looks over contacts-ac!independently ofthe former contacts. Contacts (102. prepare to connectan earth to the wire ld leading to the distributor circuit DD to releasethe relay T thereof when the call is released from the display. Contactsa.c3 prepare anjenergizingcircuit for the magnet BADM,and contacts (104prepare an energizing circuit for the magnet ABDM. Contacts ac5 preparea circuit for the upper coil ofrelay ST and contacts act prepare acircuit-for the lower coil of this relay. 'Relay EN also operates overits left hand coil in parallel with lamp I. At

contacts e112 a further point is prepared in the circuit for relay ST.At contacts enl (see CC Fig.

1) the earth for the normal testing operations of the relays .T in' thedistributors is removed from all connecting circuits associated with thedistributor switches so that distributors searching for a connectingcircuit in response to fresh calls are prevented from testing in-whilstcallsare waiting on the display lamps.

The distributor switches D and their associated circuits over whichsucceeding calls are made are caused to test into and associatethemselves with the relays BJ which operate in succession as callsarrive and at their respective contacts-4 and 5 close the circuits forthe lamps DOP2--O over the arcs ab'l-ab8 and similar arcs of the switchBA, that is, provided meanwhile no calls have been answered. When themaximum number of calls are queued up on the display lamps,

. and therefore relay J operated, further searching switches test intothe lead OF which extends to the callmeter CM over contacts 9'3 and arc(1125, the call meter indicating the number of calls so connected. Theresistance in the connection from each distributor circuit to the leadOF is individual to the distributor circuit so that the relays T ofother searching distributors are not affected and can freely test intothe lead OF.

It will-be seen that providing the switches AB and BA arestanding incorrespondingpositions a circuit is closed over arcs ab2 and bal forrelay SY which at contacts syl opens the self drive circuit for themagnet BADM. Upon an operator assigning a connecting circuit by throwingthe speaking key SPK associated with the connecting circuit and bythrowing the connect answer key CA.v in the position circuit OPC, acircuit is completed from earth, over contacts CA2, relay CN, contactscgl, mnl,

(relay MN being operated at this time in series with relay SL Fig. 1),e112, acfi, stl, lower coil of relay ST to battery and relay ST operatesand locks itself over its upper coil and contacts st2,;

and ac5. When contacts stl are in the mid position relay CN which is avery fast operating relay :operates in series with the resistance andcloses a circuit in serieswith itself for-coil (II) of relay CG overcontacts c'nl but this coil is shunted for,

the moment. Relay CG operates when contacts stl change over and atcontacts cgl opens a point in the operating circuit for the lower coilof relay ST;

A further point in the operating circuit for the;

lower coil of relay ST is opened at contacts stl and this coil, beingshunted, gives the relayslow releasing characteristics. r 7

Thus the signal transmitted from the operators circuit OPC to the relayST is of very short dura-.:

tion and occupies only a part of the movement of the contacts stl, thisminimizing the chances of the simultaneous connection of two operatorspositions to the'display circuit.

A circuit is closed from earth over-contacts syl, ac3, std, magnet'BADM' to negative and'the magnet energizes. 'A circuit isalso closedfrom ,earth overcontacts (104, stE, arc abl, magnet ABDM to battery'andthis magnet energizes. I At contacts stB a point in the originaloperating circuit for relay AC is opened, but this relay holds overcontacts acl.

Anearth is extended over contacts (102, $153, col, arc ab3, to relay Ashort circuiting this relay and also relay T in the distributor-circuitboth of which relays release.

magnet LM to battery and the magnet energizes to close the circuit ofthe driving motor and the wipers of the switch are advanced to the homeposition where the contacts onl open releasing 'relay WS which in turnreleases relay TCO at:

contacts 1086. Upon the relapse of relay TCO the circuit for the magnetLM is completed over contacts tl, sl, tcofi and b4 and the wipers aredriven in search of the assigned connecting circuit, and when this isfound relay T'operates' from earth over contacts tco'l, ds3, b3,rectifier R, relay T, contacts ws5 and over arc 4 or 4a. Relay T onoperation allows relay S to operate and the operations as beforedescribed take place.

When relay A in the lamp display circuit Fig. 2

releases the circuit for the lamp DOPI and for :relay AC is opened atcontacts at and a5, and

relay AC releases. At contacts act and ac the circuits for the magnetsvBADM and. ABDM are opened and the wipers of the switches BA and AB arestepped. The short circuit is removed from relay A at contacts ac2. Theholding circuit for the upper coil of relay ST is opened at contacts ac5but relay ST does not release -im,;

mediately as it is rendered slow to release by virtue of its shuntedlower coil so that the circuit to the operators circuit is maintainedopen at contacts stl for a short period to enable the apparatus in thedisplay circuit to function correctly.

As the call of the first order of priority has been answered it isnecessary that the other calls that are queued up on the display lampsshould all be moved up one in their order of priority. This isaccomplished over the arcs abfi, ab! etc. It will be seen that when theswitch AB steps a circuit is closed over contacts b and b5, secondcontact of arc ab! to lamp DOPI and to relay AC in parallel therewithwhen relay ST releases. Thus the call of the second order of priority ismoved into the first place, whilst the third call lighting the lamp DOP3is moved into second place and associated with the lamp DOP2 and so on.

When the switch AB steps the circuit to the lead OF is broken at arc ab5and the wipers are stepped on to the contacts connected to the contactsa3. Thus all of the T relays in the distributors held over the lead OFare released and the associated switches search for the free displaylamp circuits, one of the distributors seizing the circuit of the freedrelay A whilst the unsuccessful switches continue in operation untilthey again test into the lead OF over contacts 113, arc'ab5, and thecall meter CM.

When the operator has dealt with the call the key CA is restoredreleasing relays CN and CG and that portion of the position circuitshown in Fig. 2 is restored to normal.

It will be seen that under normal operating conditions when no callsexist on the calling lamps, and relay EN is normal, relay CO is operatedon the operation of the key CA and at contacts col opens a point in thetest circuit into the display circuit. 7

When seven calls exist on the calling lamps DOP a circuit is closed forrelay ON over its right hand coil in parallel with the lamp 1 and relayON operates and locks over its left hand coil in parallel withlamp 6. Anearth is connected over contacts 001122, 0712, to the lead AL leading tothe lamp display circuits on one or more relief or omnibus positionswhereby the operators on these positions are signalled to assist in theanswering of the calls. Relay ON is released when the number of callsfalls below six.

In the event of nine calls becoming queued up a circuit is closed forthe right hand coil of relay OM in parallel with the calling lamp 9 andrelay OM operates and closes at contact cm! a circuit for its left handcoil' in parallel with lamp 8.

At contacts omZ a circuit is closed for relay AA at one or more furtherrelief or omnibus positions, the operating earth being derived overcontacts oomZ which are contacts of a relay similar to relay OM butwhich is associated with the display lamps on an omnibus position, sothat if more than a certain number of incoming calls are signalled inthis position the omnibus positions cannot be called to assist inhandling the traffic on the demand position.

Relay AA operates and at contacts cal to aalfl connects the demanddisplay lamps on the omnibus position OOP in parallel with the displaylamps on the demand position so that the, corresponding lamps light. Thecircuits for the incoming lamps on the omnibus position are disconnectedat contacts call to aa20. Thus an omnibus operator is called to assistthe demand operators and may answer the calls in an eX- actly similarmanner to that previously described, the omnibus operator havingconnecting circuits associated with the demand distributor circuits.

At contacts aaZl a circuit is closed over the wire SP for a supervisorydevice to indicate the state of congestion to a supervisory operator.When the number of queued calls fall below eight relay OM is releasedreleasing relay AA, and the demand calling lamps on the omnibus positionare disconnected and the incoming lamps reconnected.

If however nine or more incoming calls are queued up on the incomingcalling lamp display on the omnibus position a relay, say OOM similar torelay OM in LDC associated with that display will be operated andcontacts oomZ will be open. Thus it will not be possible to interruptthe incoming 'traflic to the omnibus operators position until some ofthe incoming traffic has been dealt with. 7

In order that calls are'not held beyond a certain period during the timethat insufiicient calls' are in the queue to signal the omnibus positionthere is associated with each of the relays AJ of the lamp displaycircuit LDC two relays, such as relays SA and ZA, only those relaysassociated with the relay A however being shown, the other pairs beingconnected and operated in an identical manner.

Two contacts a6 and a1 control the operation of the relays SA and ZA,and as all of the other relays BJ are provided with similar contacts,which however are not shown, the relays are designated as having sevencontacts.

Earthed impulses are periodically and alternately delivered over theleads S and Z.

Assuming that a call is held on relay A over a period during which theimpulses are delivered to the leads S and Z,then, when the impulse isgiven over the lead S a circuit is closed for the right hand coil ofrelay SA over contacts 2112 and a6, and relay SA operates, and looksover its left hand coil, contacts a'!, left hand coil of relay ZA, andcontacts sal. Relay ZA will not operate in this circuit. When theimpulse occurs over the lead Z relay ZA operates over its right handcoil and contacts 8112. At contacts zal a locking circuit is closed forrelay ZA over its left hand coil and the left hand coil of relay SA isshort circuited making the relay slightly slow to release. The circuitfor the right hand coil of relay SA is opened at contacts zaZ and aftera short period relay SA releases. A circuit is closed for relay DL atcontacts 203, and relay DL operates.

At contacts all! a circuit is closed for relay AA, and at contacts (H2an earth is applied to the lead AL to operate similar relays such as AAon the relief positions.

The switches AB and BA are stepped in the manner described to alter theposition of the calls in the queue until the switch AB is stepped to thetwenty first contact whereupon a circuit is closed from earth overcontacts abdm, arc and wiper ab! magnet ABDM to battery and the switchAB is stepped to its normal position under the control of itsinterrupter contacts. Immediately the wiper of are (1112 steps out ofalignment with the wiper of arc bal relay SY releases and at contactssyl closes the circuit for magnet BADM and the switch BA homes whereuponrelay SY operates and opens the homing circuit for magnet BADM atcontacts syl.

The common relays NA in the lamp display circuits are night alarm relaysadapted to operate when any lamp is alight to operate an alarm.

We claim:

1. In a telephone system, a group of connective circuits, a group ofhunting switches of the homing type having access to said circuits asfirst choice, a group of overflow circuits accessible to said switchesas second choice, whereby switches operated at times when no connectivecircuits are available will connect with successive overflow circuits,and controlling means operating on switches connected with overflowcircuits in the order in which the connections are established forreleasing a connected switch and for causing it to rehunt over saidconnective circuits each time a connective circuit becomes idle.

2. In a telephone system, a group of individual overflow circuits,automatic switches having access to said circuits if no regular outletsare available, means for making each individual overflow circuit busywhen seized, a common overflow circuit which is not made busy whenseized and which may therefore be occupied by a number of switches whenthe individual overflow circuits are all busy, means for successivelyreleasing the switches connected to individual overflow circuits, andmeans effective whenever an individual overflow circuit is freed forcausing the switches connected to the common overflow circuit to huntfor the free individual overflow circuit.

3. In a telephone system, a group of automatic switches, a group ofconnective circuits accessible to said switches, a group of individualoverflow circuits accessible to said switches only if none of saidconnective circuits are available, a common overflow circuit accessibleto said switches only if all said individual overflow circuits are busy,means operative at a time when one or more switches are connected to thecommon overflow circuit and responsive to a connective circuit becomingavailable for releasing one switch connected to an individual overflowcircuit and for causing it to hunt for the available connective cirrcult, and means for releasing all switches connected to said commonoverflow circuit and for causing them to hunt for the free individualoverflow circuit.

4. In a telephone system, a group of overflow circuits, at correspondinggroup of lamps, switches having access to said circuits, means forbusying each circuit when seized and for lighting the correspondinglamp, means for releasing switches from overflow circuits one at a time,and means intervening between the said circuits and lamps and operativeevery time a switch is released for changing the relation between saidcircuits and said lamps to associate each circuit with a different lamp.

5. In a telephone system, a group of relays numbered consecutively, agroup of lamps correspondingly numbered, means for energizing saidrelays in the order of their numbering to light the corresponding lamps,means for releasing said'relays in the same order, and means operativeeach time a relay is released for shifting each relay into associationwith the next lower numbered lamp.

6. In a telephone system, a plurality of connective circuits common to aplurality of operators, automatic switches having access to saidcircuits, circuit arrangements such that the connective circuits arenormally unselectable by said switches and are individually madeavailable for selection when the operator handling the calls is ready totake a call, overflow circuits accessible to said switches at times whenno connective circuits are available for selection, and means responsiveto a predetermined number of overflow circuits becoming occupied forautomatically signalling another one of said operators to assist inhandling the calls.

'7. In a telephone system, a plurality of connective circuits common toa plurality of operators,

automatic switches having access to said cir- .2.)

cuits, circuit arrangements such that the connective circuits arenormally unselectable by said switches and are individually madeavailable for selection when the operator handling the calls is ready totake a call, overflow circuits accessible to said switches at times whenno connective circuits are available for selection, means forsuccessively releasing switches from overflow circuits to permit them tohunt for connective circuits as the latter are made available by theoperator, and means for automatically signalling another operator if aswitch remains connected to an overflow circuit for a predeterminedtime. BERNARD ANTHONY HENSLER. CHARLES LEONARD PETERS.

